1. Field of the Invention
The present invention relates to a mobile terminal and, particularly, to a system and a method for receiving a broad-band signal in a mobile terminal.
2. Description of the Background Art
A software defined radio (SDR) is a technology for realizing various functions in a mobile communication system by implementing software solutions for programmable hardware devices. Due to the analog communication technology being abandoned in favor of it's digital counterpart, SDR technology is becoming more popular and useful. The SDR technology accommodates various communication standards in one terminal. The SDR technology makes it possible for a wireless interface to be constructed by way of a software wirelessly downloadable to the mobile terminal. Various communication methods may be supported in real-time by request of a user or by a network manager in a single platform.
Furthermore, SDR uses programmable hardware in which most function blocks including the RF region are operated by software modules for controlling high speed processors. Therefore, a multiple radio access standard or service function can be supplied only by reprogramming the hardware instead of replacing it. In addition, when various mobile communication services are provided to a terminal or to a base station using the SDR, a user is provided with various communication services at a low cost regardless of local standard of the mobile communication system or the kind of service provided.
Further, a user may be provided with options for services suitable to the user's personal preferences. An SDR terminal may support discretionary radio communications and various protocols such as global system for mobile communication (GSM), code division multiple access (CDMA), time division multiple access (TDMA), and global positioning system (GPS).
FIG. 1 is a block diagram showing a signal receiving apparatus in a general SDR terminal. As shown, the signal receiving apparatus of a general SDR terminal comprises: an antenna 10 for receiving an analog radio frequency (RF) signal through a radio section; a send/receive signal processing unit 20 for dividing the analog RF signal into a high frequency analog RF signal and a low frequency analog RF signal, and generating a switch control signal; a first switch 30A and a second switch 30B controlled by the switch control signal transmitted from the send/receive signal processing unit 20; a high frequency pass unit 40 for converting the received high frequency analog RF signal into a high frequency digital RF signal; a low frequency pass unit 50 for converting the received low frequency analog RF signal into a low frequency digital RF signal; a digital signal processing unit 60 for processing the digital RF signal transmitted from the second switch 30B; and an input/output unit (I/O unit) 70 for providing the digital RF signal transmitted from the digital signal processing unit 60.
The high frequency pass unit 40 comprises: a high-pass filter (HPF) 41 for filtering the received high frequency analog RF signal to a baseband frequency; a low noise amplifier (LNA) 42 for amplifying the filtered high frequency analog RF signal in order to reduce noise factor of the entire receiver; and a high frequency A/D converter 43 for converting the amplified high frequency analog signal into a high frequency digital RF signal. The low frequency pass unit 50 comprises: a low-pass filter (LPF) 51 for filtering the received low frequency analog RF signal to a predetermined frequency band; a low noise amplifier 52 for amplifying the filtered low frequency analog RF signal in order to reduce the noise factor of the entire receiver; and an low frequency A/D converter 53 for converting the amplified low frequency analog RF signal into a low frequency digital RF signal.
FIG. 2 is a flow diagram illustrating a method of operation in the signal receiving apparatus of a general SDR terminal. Referring to FIGS. 1 and 2, at step S200, the antenna 10 receives an analog RF signal and transmits it-to the send/receive signal processing unit 20. The send/receive signal processing unit 20 determines the kind of signal and whether the received analog RF signal is a high or low frequency signal, at steps S210 and S220 respectively.
If the analog RF signal is a high frequency signal, the send/receive signal processing unit 20 generates a switch control signal for controlling the switch toward the high frequency pass unit 40, at step S230, and transmits the control signal to the first switch 30A and to the second switch 30B. Then the first switch 30A and the second switch 30B are controlled toward the high frequency pass unit 40, at step S240. Thereafter, the send/receive signal processing unit 20 transmits the high frequency analog RF signal to the high frequency pass unit 40.
The high frequency analog RF signal is fed to the high-pass filter 41. The high-pass filter 41 filters the received high frequency analog RF signal to a baseband frequency, and transmits the filtered high frequency analog RF signal to the low noise amplifier 42, at step S250, for amplification. The LNA 42 amplifies the high frequency analog RF signal in order to reduce the noise factor of the entire receiver, and transmits the amplified high frequency analog RF signal to the A/D converter 43. The high frequency A/D converter 43 converts the received high frequency analog RF signal into a low frequency digital RF signal, at step S260, and thereafter transmits the signal to the digital signal processing unit 60.
Referring back to step S220, if the received analog RF signal is a low frequency signal, then the send/receive signal processing unit 20 generates a switch control signal for controlling the switch toward the low frequency pass unit 45, at step S290. The control signal is provided to the first and second switches 30A and 30B, at step S300, to control the switch toward the low frequency pass unit. As such, the send/receive signal processing unit 20 transmits the low frequency analog RF signal to the low frequency pass unit 50.
The low frequency analog RF signal is then provided to the low pass filter (LPF) 51. The LPF 51 filters the low frequency analog RF signal to a baseband frequency, and transmits the filtered low frequency analog RF signal to the low noise amplifier (LNA) 52, at step S250, for amplification. The LNA 52 amplifies the low frequency analog RF signal in order to reduce the noise factor of the entire receiver, and transmits the amplified low frequency analog signal to the low frequency A/D converter 53. The low frequency A/D converter 53 converts the received low frequency analog RF signal into a low frequency digital RF signal, and transmits the signal to the digital signal processing unit 60 through the second switch 30B, at step S260.
Referring to FIG. 1, the digital signal processing unit 60 receives the high or low frequency digital RF signal and processes the digital RF signal, at step S270. The digital RF signal is then transmitted to the I/O unit 70. At step S280, the I/O unit 70 provides the digital RF signal as output.
As such, the signal receiving apparatus in a general SDR terminal converts an analog RF signal into a digital RF signal using two separate high and low frequency A/D converters 43 and 53, respectively. After the conversion then the digital signal is processed by digital signal processing unit 60. Therefore, the signal can be only converted and processed in a frequency range specific to the high and low A/D converters 43 and 53. Consequently, the operation frequency range in which the signal receiving apparatus in the SDR terminal can operate is limited.